Reductive Degradation of CCl by Sulfidized Fe and Pd-Fe Nanoparticles: Kinetics, Longevity, and Morphology Aspects.

In this study a systematic comparison in morphology, long-term degradation, regeneration and reuse were conducted between palladized and sulfidized nanoscale zero-valent iron (Pd-Fe and S-Fe). Pd-Fe and S-Fe were prepared, after the synthesis of precursor Fe nanoparticles (spherical, ~35 nm radius) for carbon tetrachloride (CTC) treatment. With HAADF-TEM-EDS characterization, dispersive Pd islets were found on the Fe core of Pd-Fe. However, the Fe core was covered by the FeS shell of S-Fe (FeS/FeS = 0.47). With an excessive Pd dose (10 mol%), the Pd-Fe were dramatically deformed to dendritic structures which significantly decreased reactivity. For CTC degradation, Pd-Fe (0.3 atomic% Pd) increased the degradation rate by 20-fold (k= 0.580 Lmmin) while S-Fe presented a greater life time. The major intermediate chloroform (CF) was further degraded and less than 5% CF was observed after 24 h using Pd-Fe or S-Fe while above 50% CF remained using Fe. During aging, the Fe core was converted to FeOOH and FeO/γ-FeO. The restoration of Fe was achieved using NaBH, which regenerated Fe and Pd-Fe. However, the formed FeS shell on S-Fe was disappeared. The results suggest that S-Fe extends longevity of Fe, but the loss of FeS after aging makes S-Fe eventually perform like Fe in terms of CTC degradation.